CN114616411A

CN114616411A - Power transmission device

Info

Publication number: CN114616411A
Application number: CN202080075335.3A
Authority: CN
Inventors: 迫田裕成; 千原佑太; 三轮拓弥
Original assignee: NSK Ltd
Current assignee: NSK Ltd
Priority date: 2019-11-07
Filing date: 2020-11-06
Publication date: 2022-06-10
Also published as: EP4056865A1; US20220403921A1; EP4056865A4; JP2021076177A; WO2021090907A1; KR20220076512A

Abstract

The power transmission device of the present invention includes: a housing; a ball screw device having a nut housed in the housing, a screw shaft penetrating the nut, and balls disposed between the nut and the screw shaft; a first bearing and a second bearing which are provided between the housing and the nut and are adjacent to each other in a central axis direction parallel to a central axis of the nut; and a preload-applying member formed of an elastic body, for applying preload to the first bearing and the second bearing; the first bearing and the second bearing each include an outer ring fitted to the housing and spaced apart from each other in the center axis direction; the first bearing and the second bearing are configured to be in a face-to-face configuration; the preload-applying member presses the outer rings in a direction in which the outer rings approach each other, and a gap is formed between the outer rings.

Description

Power transmission device

Technical Field

The present invention relates to a power transmission device.

Background

As one of the electric power steering apparatuses, a rack assist type electric power steering apparatus is exemplified. The rack assist type electric power steering apparatus of patent document 1 includes a power transmission device for transmitting power of an electric motor to a rack. The power transmission device of patent document 1 includes a ball screw device for converting a rotational motion of a motor into a linear motion of a rack. The ball screw device includes: the screw shaft is integrally formed with the rack, the nut is penetrated by the screw shaft, and the plurality of balls are arranged between the first groove of the screw shaft and the second groove of the nut. The power transmission device of patent document 1 further includes a double-row bearing for supporting the nut.

Patent document 1: japanese patent laid-open publication No. 2018-70117

Disclosure of Invention

When a powerful torque load is input to the bearing, the torque load acts on the ball screw device disposed on the inner peripheral side of the bearing as a reaction thereof. The bearing of patent document 1 is configured to be arranged back to back with a large pitch of the operating points, and has high rigidity against moment load. That is, the moment load input as a reaction to the ball screw device is also large. The ball screw device is a member that exclusively copes with axial loads, and if a large moment load is input, there is a possibility that abnormal noise may occur, which is not preferable.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a power transmission device capable of reducing a moment load input to a ball screw device while applying a stable preload to a bearing ring.

In order to achieve the above object, a power transmission device according to one aspect of the present invention includes: a housing; a ball screw device having a nut accommodated in the housing, a screw shaft penetrating the nut, and balls disposed between the nut and the screw shaft; a first bearing and a second bearing which are provided between the housing and the nut and are arranged adjacent to each other in a central axis direction parallel to a central axis of the nut so as to face each other; and a preload-applying member that applies preload to the first bearing and the second bearing, wherein the first bearing and the second bearing each include an outer ring that is fitted in the housing and spaced apart from each other in the central axis direction, and the preload-applying member presses the outer rings in a direction in which the outer rings approach each other, and a gap is formed between the outer rings.

When there is a dimensional error in the central axis direction in the outer rings, the dimensional error enters the gap between the outer rings and is absorbed. Therefore, the outer ring does not displace in the central axis direction, and the load acting on the rolling elements is only a load applied by being pressed by the preload application member. As a result, a predetermined preload amount is obtained, and a stable preload can be applied to the bearing ring. In addition, the first bearing and the second bearing are arranged in a face-to-face manner with a small distance between the points of action. That is, the first and second bearings are less stiff with respect to moment loads. Therefore, the torque load input to the ball screw device is reduced, and the occurrence of the abnormal noise is suppressed.

As a preferred aspect of the power transmission device of one aspect, the power transmission device further includes: and an inner ring having a first inner ring raceway surface on which the rolling elements roll between the inner ring and the outer ring of the first bearing, and having a second inner ring raceway surface on which the rolling elements roll between the inner ring and the outer ring of the second bearing. This reduces the number of parts and the number of man-hours for mounting work.

In a preferred embodiment of the power transmission device of one aspect, the nut has two hardened inner race raceway surfaces on an outer peripheral surface thereof, on which the rolling elements roll. Thus, the inner ring can be omitted, and the power transmission device can be downsized in the radial direction. In addition, the surface of the inner ring raceway surface has a certain hardness, and the durability is improved.

In a preferred embodiment of the power transmission device of one aspect, the outer peripheral surface of the outer ring is formed with a grease groove recessed inward in the radial direction. This ensures more grease, improves the sliding property of the outer ring, and prevents frictional heat from being generated. Therefore, the fluctuation of the preload due to the thermal expansion of the outer ring can be suppressed.

In a preferred embodiment of the power transmission device of one aspect, an O-ring is provided between an outer peripheral surface of the outer ring and the housing. Since the O-ring absorbs radial vibration of the outer ring, occurrence of so-called rattle noise (rattle noise) is suppressed.

In a preferred embodiment of the power transmission device of one aspect, a cylindrical cushion member is disposed between the outer peripheral surface of the outer ring and the housing, and the outer peripheral surface of the outer ring is covered with the cushion member. The shock absorbing member can absorb large vibration that cannot be completely absorbed by the O-ring, and can reliably suppress the occurrence of so-called knocking noise.

In a preferred embodiment of the power transmission device according to one aspect, the preload-applying member is an elastic body made of a metal material, and the outer ring has a projection projecting from an end surface thereof and provided between the housing and the preload-applying member. Thereby, the elastic body of the metal material is in contact with the projection. Therefore, the elastic body of the metal material can be prevented from contacting the housing to wear the housing.

In a preferred embodiment of the power transmission device according to one aspect, either one of the first bearing and the second bearing is provided with an inner peripheral seal member that closes a gap between an inner peripheral surface of the outer ring and an opposing surface that opposes the inner peripheral surface of the outer ring. Therefore, the foreign matter is not easily intruded into the first bearing or the second bearing.

In a preferred embodiment of the power transmission device of one aspect, the inner peripheral seal member includes: an inner periphery sealing core bar disposed on an inner periphery side of the outer ring; and an inner peripheral sealing elastic body supported by the inner peripheral sealing core and slidably contacting the opposing surface, the preload-applying member including: an elastic body for pre-compaction for generating pre-compaction: and a preload core for supporting the preload elastomer, the inner peripheral seal core having an inner peripheral fitting portion fitted to an inner peripheral surface of the outer ring and being formed integrally with the preload core. Thus, the inner peripheral seal member and the preload application member can be attached to each other by the operation of fitting the inner peripheral seal core metal into the inner peripheral side of the outer ring. Thus reducing man-hours for the mounting work.

A preferred embodiment of the power transmission device according to one aspect includes: and an outer circumferential sealing elastic body that closes a gap between an outer circumferential surface of the outer ring and an inner circumferential surface of the housing, the outer circumferential sealing elastic body being fixed to an outer circumferential surface of the preload core and being in sliding contact with the inner circumferential surface of the housing. The outer peripheral sealing elastic body can prevent grease from leaking between the housing and the outer ring, and ensure the sliding property of the outer ring. Further, since the outer peripheral sealing elastic body absorbs the radial vibration of the outer ring, the occurrence of so-called rattling noise is suppressed. Further, the three members of the inner peripheral seal member, the preload application member, and the outer peripheral seal elastic body can be attached by the work of fitting the inner peripheral seal core into the inner peripheral side of the outer ring, and the man-hours of the attachment work can be reduced.

A preferred embodiment of the power transmission device according to one aspect includes: a core bar fixed to an outer ring of either one of the first bearing and the second bearing; and an inner peripheral sealing elastic body supported by the core metal to close an inner peripheral side of the outer ring, wherein the core metal has a cylindrical outer peripheral fitting portion fitted to an outer peripheral surface of the outer ring, and the outer peripheral surface of the outer ring has a recess recessed inward in a radial direction for receiving the outer peripheral fitting portion. Thus, the outer peripheral fitting portion is accommodated in the recess, and the outer peripheral fitting portion can be prevented from abutting against the housing and inhibiting the sliding of the outer ring.

A preferable aspect of the power transmission device according to one aspect includes: and an outer peripheral sealing elastic body that closes a gap between an outer peripheral surface of the outer ring and an inner peripheral surface of the housing, the outer peripheral sealing elastic body being fixed to an outer peripheral surface of the outer peripheral fitting portion and being in sliding contact with the inner peripheral surface of the housing. The outer peripheral sealing elastic body can prevent grease from leaking between the housing and the outer ring, and ensure the sliding property of the outer ring. Further, since the outer peripheral sealing elastic body absorbs the radial vibration of the outer ring, the occurrence of so-called rattling noise is suppressed. Further, when the core is attached to the outer ring, the outer periphery sealing elastic body is also attached together, and therefore, the number of attachment steps is reduced.

A preferred embodiment of the power transmission device according to one aspect includes: and a high load absorbing portion provided between the preload application member and the outer ring, for absorbing a high load in the central axis direction, wherein a cross-sectional area of the preload application member cut in the central axis direction is smaller than the high load absorbing portion. Thus, when the high-load absorbing portion and the preload-applying member are attached, the preload-applying member deforms and presses the outer ring, thereby applying a preload to the bearing. On the other hand, when the ball screw device receives a high load, the high load absorbing portion absorbs the high load. Thereby avoiding a situation in which the pre-compression applying member is broken by a high load.

In a preferred embodiment of the power transmission device according to one aspect, the preload application member includes a plurality of protrusions arranged to be spaced apart from each other in the circumferential direction. According to this structure, the preload amount of the preload-applying member can be adjusted by changing the number of the convex portions.

The power transmission device of the invention can apply stable pre-pressure to the bearing ring and reduce the moment load input to the ball screw device.

Drawings

Fig. 1 is a schematic diagram of an electric power steering apparatus having a power transmission device according to embodiment 1.

Fig. 2 is a front view of the rack gear of embodiment 1.

Fig. 3 is a sectional view of the power transmission device according to embodiment 1.

Fig. 4 is an enlarged sectional view of the periphery of the bearing of fig. 3.

Fig. 5 is a sectional view illustrating an extension line of a contact angle of the first bearing and the second bearing.

Fig. 6 is a sectional view of a power transmission device according to modification 1.

Fig. 7 is a sectional view of a power transmission device according to modification 2.

Fig. 8 is a sectional view of the power transmission device according to embodiment 2.

Fig. 9 is a sectional view of a power transmission device according to embodiment 3.

Fig. 10 is a sectional view of a power transmission device according to embodiment 4.

Fig. 11 is a cross-sectional view of the power transmission device of embodiment 5.

Fig. 12 is a sectional view of a power transmission device according to modification 3.

Fig. 13 is a sectional view of a power transmission device according to embodiment 6.

Fig. 14 is a sectional view of a power transmission device according to embodiment 7.

Fig. 15 is a sectional view of a power transmission device according to embodiment 8.

Fig. 16 is a sectional view of a power transmission device according to embodiment 9.

Fig. 17 is a schematic view of only the pre-pressure applying member and the high load absorbing portion of fig. 16 extracted and viewed from the central axis direction.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiment (hereinafter, referred to as embodiment) for carrying out the present invention described below. Further, the structural elements in the following embodiments include those which are substantially the same and are within the range of so-called equivalents, as can be easily conceived by those skilled in the art. Further, the constituent elements disclosed in the following embodiments may be appropriately combined.

Embodiment mode 1

Fig. 1 is a schematic view of an electric power steering apparatus having a ball screw device according to embodiment 1. As shown in fig. 1, the electric power steering apparatus 80 includes: a steering wheel 81, a steering shaft 82, a universal joint 84, a lower shaft 85, a universal joint 86, a pinion shaft 87, a pinion 88a, and a rack 88 b.

The steering wheel 81 is connected to a steering shaft 82. One end of the steering shaft 82 is connected to the steering wheel 81. The other end of the steering shaft 82 is connected to a universal joint 84. One end of the lower shaft 85 is connected to the steering shaft 82 via a universal joint 84. The other end of the lower shaft 85 is connected to a pinion shaft 87 through a universal joint 86. The pinion shaft 87 is connected to a pinion gear 88 a. The pinion gear 88a is engaged with the rack gear 88 b. When the pinion gear 88a rotates, the rack gear 88b moves in the vehicle width direction of the vehicle. The pinion gear 88a and the rack gear 88b convert the rotational motion transmitted to the pinion shaft 87 into linear motion. Both ends of the rack 88b are connected to tie rods 89. The angle of the wheel changes according to the movement of the rack 88 b. Further, the operation of the steering wheel 81 may be converted into an electric signal, and the angle of the wheel may be changed by the electric signal. That is, a steer-by-wire (Steer-by-wire) system may be applied to the electric power steering device 80.

The electric power steering apparatus 80 further includes an electric motor 93, a torque sensor 94, and an ECU (Electronic Control Unit) 90. The motor 93 is, for example, a brushless motor, but may be a motor having a brush (brush) and a commutator (commutator). The motor 93 is disposed in a housing 100 described later. The torque sensor 94 is mounted on the gear 88a, for example. The torque sensor 94 outputs the steering torque transmitted to the pinion gear 88a to the ECU90 through CAN (Controller Area Network) communication. The vehicle speed sensor 95 detects a traveling speed (vehicle speed) of a vehicle equipped with the electric power steering device 80. The vehicle speed sensor 95 is disposed on the vehicle body, and outputs a running speed (vehicle speed) to the ECU90 by CAN communication. The motor 93, the torque sensor 94, and the vehicle speed sensor 95 are electrically connected to the ECU 90.

The ECU90 controls the operation of the motor 93. The ECU90 acquires signals from the torque sensor 94 and the vehicle speed sensor 95, respectively. In a state where ignition switch 98 is on, power supply device 99 (for example, an in-vehicle battery) supplies power to ECU 90. The ECU90 calculates an assist steering command value based on the steering torque and the vehicle speed. The ECU90 adjusts the power value supplied to the electric motor 93 based on the assist steering command value. The ECU90 acquires information on the induced voltage from the motor 93 or information output from a resolver or the like provided in the motor 93.

Fig. 2 is a front view of the rack gear of embodiment 1. Fig. 3 is a sectional view of the power transmission device according to embodiment 1. Fig. 4 is an enlarged cross-sectional view showing the periphery of the bearing of fig. 3. Fig. 5 is a cross-sectional view illustrating an extension of a contact angle of the first bearing and the second bearing. As shown in fig. 2, the housing 100 is a tubular member extending in the vehicle width direction. The case 100 is formed of a light metal such as an aluminum alloy or a magnesium alloy. The housing 100 includes a first body 101, a second body 103, and a third body 105. The first body 101, the second body 103 and the third body 105 are connected into a whole by bolts.

As shown in fig. 3, the power transmission device 1 is housed in the first body 101. The second body 103 houses the pulley device 20. The third body 105 houses the motor 93.

The power transmission device 1 includes a first body 101 of a housing 100, a ball screw device 10, a plate 18, a first bearing 30a, a second bearing 30b, and preload

application members

40a and 40 b. The ball screw device 10 includes a screw shaft 11, a nut 13, and balls 15.

A second thread groove 12 is formed in the outer peripheral surface of the screw shaft 11. The threaded shaft 11 extends in the vehicle width direction and penetrates the nut 13. The screw shaft 11 is a part of the rack 88 b. That is, the screw shaft 11 is formed integrally with the rack 88 b.

The inner peripheral surface of the nut 13 is formed with a first thread groove 14. The nut 13 is supported by the first bearing 30a and the second bearing 30b and is rotatable about the central axis AX. A plurality of balls 15 are arranged between the first thread groove 14 of the nut 13 and the second thread groove 12 of the screw shaft 11. The balls 15 circulate endlessly on a rolling path formed by the first thread groove 14 of the nut 13 and the second thread groove 12 of the screw shaft 11. Therefore, when the nut 13 is rotated, the threaded shaft 11 (rack 88b) moves in the vehicle width direction. Thereby, the rotational motion is converted into the linear motion of the rack 88 b.

In the following description, a direction parallel to the central axis AX of the nut 13 is referred to as a central axis AX direction. In the direction of the central axis AX, the direction in which the second body 103 is disposed is referred to as a first direction side (left side in fig. 3) of the direction of the central axis AX, and the direction opposite to the direction in which the second body 103 is disposed is referred to as a second direction side (right side in fig. 3) when viewed from the inside of the first body 101. The direction perpendicular to the central axis AX is simply referred to as a radial direction. Radial is a direction sometimes referred to as the radial direction.

The pulley device 20 transmits the power of the motor 93 to the nut 13. The pulley device 20 includes a drive pulley 21, a driven pulley 23, and a transmission belt 25. The drive pulley 21 is fixed to an output shaft 93a of the motor 93. The driven pulley 23 is fixed to the nut 13 and rotates integrally with the nut 13. The transmission belt 25 is an endless belt and is disposed across the drive pulley 21 and the driven pulley 23.

According to the above configuration, when the motor 93 is rotationally driven, the power generated by the motor 93 is transmitted to the nut 13 via the pulley device 20. Then, the nut 13 supported by the first bearing 30a and the second bearing 30b is rotated. When the nut 13 rotates, an axial force acts on the rack 88b (the screw shaft 11). Thereby, the force of the gear 88a (steering wheel 81) required for moving the rack 88b becomes small. That is, the electric power steering apparatus 80 adopts a rack assist system.

The plate 18 is an annular member for preventing the first bearing 30a, the second bearing 30b, and the

preload application members

40a and 40b from falling out of the first body 101. The plate member 18 is housed in a recess 101a formed in an end surface of the first body 101 facing the first direction side. Further, a projection 103a projecting from an end surface of the second body 103 facing the second direction side abuts the plate member 18 to restrain the plate member 18 from falling off the recess 101 a.

As shown in fig. 4, the first bearing 30a and the second bearing 30b are both angular contact ball bearings. The first bearing 30a and the second bearing 30b are disposed between the first body 101 and the nut 13. The first bearing 30a and the second bearing 30b are disposed adjacent to each other in the direction of the central axis AX. The first bearing 30a and the second bearing 30b are disposed so as to face each other. The first bearing 30a and the second bearing 30b include

outer rings

31a, 31b,

inner rings

33a, 33b, and a plurality of rolling

elements

35a, 35b, respectively.

The

outer rings

31a and 31b are fitted to the inner circumferential surface 101b of the first body 101. Specifically, the

outer rings

31a and 31b are clearance-fitted to the inner circumferential surface 101b of the first body 101. Therefore, the

outer rings

31a and 31b are slidable in the central axis AX direction with respect to the inner circumferential surface 101 b. The

outer rings

31a and 31b are pressed by the preload-applying

members

40a and 40b so as to approach each other. Specifically, the outer ring 31a is pressed toward the second direction side by the preload application member 40 a. And the outer ring 31b is pressed toward the first direction side by the pre-pressure applying member 40 b. As a result, as shown in fig. 5, the rolling elements 35a contact the outer ring raceway surface 31c and the inner ring raceway surface 33c in the first bearing 30a, and preload is applied to the first bearing 30 a. Similarly, in the second bearing 30b, the rolling elements 35b contact the outer ring raceway surface 31d and the inner ring raceway surface 33d, and preload is applied to the second bearing 30 b. Thereby, the load generated by the pressing by the

preload application members

40a and 40b acts on the rolling

elements

35a and 35b, and the internal play becomes negative. In the present embodiment, the

outer rings

31a and 31b are clearance-fitted to the inner peripheral surface 101b of the first body 101, but the inner diameter of the inner peripheral surface 101b of the first body 101 may be the same as the outer diameters of the

outer rings

31a and 31b as long as the

outer rings

31a and 31b are slidable relative to the housing 100.

Further, as shown in fig. 4, in a state where the preload is applied, the

outer rings

31a, 31b are spaced from each other in the central axis AX direction. In other words, a gap S is formed between the

outer rings

31a, 31 b. Accordingly, even if the outer shape of the outer ring 31a has a dimensional error that is larger than a predetermined size on the outer ring 31b side in the central axis AX direction, the error is absorbed by the gap S and does not contact the outer ring 31 b. On the other hand, if the outer shape of the outer ring 31a has a dimensional error that is smaller than a predetermined size on the outer ring 31b side in the central axis AX direction, only the gap S becomes larger, and the position of the other outer ring 31b does not shift. Therefore, it is possible to avoid the situation where the loads acting on the rolling

elements

35a, 35b are varied due to the contact between the

outer rings

31a, 31b and the displacement of the outer

ring raceway surfaces

31c, 31 d. Further, in the outer shape of the outer ring 31a, when the side opposite to the outer ring 31b in the center axis AX direction is formed larger or smaller than a predetermined size, the error is absorbed by the preload application member 40a, and the outer ring raceway surface 31c is not displaced in the center axis AX direction. As described above, the load of the

preload application members

40a and 40b acting on the rolling

elements

35a and 35b does not vary, and a predetermined preload amount can be obtained. That is, the preload amount applied to the first bearing 30a and the second bearing 30b is only applied by the

preload application members

40a, 40b pressing, i.e., the constant-pressure preload is achieved.

Grease is applied between the outer circumferential surfaces of the

outer rings

31a and 31b and the inner circumferential surface 101 b.

Grease grooves

36a and 36b are formed on the outer circumferential surfaces of the

outer rings

31a and 31b, and are recessed radially inward and extend in the circumferential direction. Grease is retained in the

grease grooves

36a and 36 b. Therefore, much grease is present between the outer circumferential surfaces of the

outer rings

31a and 31b and the inner circumferential surface 101 b. That is, the

outer rings

31a and 31b can slide easily with respect to the inner circumferential surface 101b, and frictional heat is not easily generated. This can suppress the fluctuation of the preload due to the thermal expansion of the

outer rings

31a and 31 b. In order to prevent the

outer rings

31a and 31b from rotating about the central axis AX with respect to the inner circumferential surface 101b (so-called bearing-run-out), key grooves may be provided on the outer circumferential surfaces or end surfaces of the

outer rings

31a and 31b, or the

outer rings

31a and 31b may be fixed with stopper pins.

Outer ring raceway surfaces 31c and 31d are formed on inner circumferential surfaces of the

outer rings

31a and 31 b. Grooves are formed in the inner circumferential surfaces of the

outer rings

31a and 31b inside the outer ring raceway surfaces 31c and 31d, and claw portions of the retainers for retaining the rolling

elements

35a and 35b are engaged with the grooves.

The

inner rings

33a and 33b are fitted to the outer peripheral surface 13a of the nut 13. Therefore, the

inner rings

33a and 33b rotate around the central axis AX together with the nut. An end surface of the inner ring 33a abuts against the wall portion 13b of the nut 13, and an end surface of the inner ring 33b abuts against the positioning member 17. The

inner rings

33a and 33b are positioned in the direction of the central axis AX by the positioning member 17 and the wall portion 13b of the nut 13. In addition, the positioning member 17 is referred to as a locknut.

The rolling

bodies

35a, 35b are spheres. As shown in fig. 5, the rolling elements 35a are disposed between the outer ring 31a and the inner ring 33a, and contact the outer ring raceway surface 31c of the outer ring 31a and the inner ring raceway surface 33c of the inner ring 33 a. A virtual line that is orthogonal to the central axis AX and passes through the center C1 of the rolling element 35a is referred to as a reference line CNa. An extension line of a virtual line connecting a tangent point P1 between the rolling element 35a and the outer ring raceway surface 31c and a tangent point P2 between the rolling element 35a and the inner ring raceway surface 33c is referred to as an extension line LC1 of the contact angle of the first bearing 30 a. An extension LC1 of the contact angle of the first bearing 30a is inclined with respect to the reference line CNa. That is, the angle of contact between the extended line LC1 and the reference line CNa is θ 1, so as to be inclined radially inward toward the second direction side in the central axis AX direction.

The rolling elements 35b are disposed between the outer ring 31b and the inner ring 33b, and contact the outer ring raceway surface 31d of the outer ring 31b and the inner ring raceway surface 33d of the inner ring 33 b. A virtual line perpendicular to the axis AX and passing through the center C2 of the rolling element 35b is referred to as a reference line CNb. An extension line of a virtual line connecting a tangent point P3 between the rolling element 35b and the outer ring raceway surface 31d and a tangent point P4 between the rolling element 35b and the inner ring raceway surface 33d is referred to as an extension line LC2 of the contact angle of the second bearing 30 b. An extension LC2 of the contact angle of the second bearing 30b is inclined with respect to the reference line CNa. That is, the angle of contact between the extended line LC2 and the reference line CNb is θ 2, which is inclined to be closer to the first direction side in the central axis AX direction as the radial direction is closer to the inner side.

With such a face-to-face arrangement, the extension LC1 of the contact angle of the first bearing 30a and the extension LC2 of the contact angle of the second bearing 30b approach each other as approaching the center axis AX. That is, the distance between the intersection LA1 (the operating point of the first bearing 30 a) of the extension LC1 of the contact angle with the first bearing 30a and the central axis AX and the intersection LA2 (the operating point of the second bearing 30 b) of the extension LC2 of the contact angle with the second bearing 30b and the central axis AX are shorter than in the case of the back-to-back arrangement. Therefore, the first bearing 30a and the second bearing 30b are low in rigidity with respect to moment load.

In the present embodiment, an intersection LA1 of the extension LC1 of the contact angle of the first bearing 30a and the central axis AX and an intersection LA2 of the extension LC2 of the contact angle of the second bearing 30b and the central axis AX overlap each other. That is, on the central axis AX, the operating point pitch between the intersection point LA1 and the intersection point LA2 is zero. According to this structure, the first bearing 30a and the second bearing 30b substantially support the ball screw device 10 at one intersection point LAX. Therefore, the first and

second bearings

30a and 30b have extremely low rigidity against moment load. Therefore, even if a moment load is input to the first bearing 30a and the second bearing 30b during the running of the vehicle, the moment load input to the ball screw device 10 as a reaction is greatly reduced. This suppresses the occurrence of abnormal noise in the ball screw device 10 due to the input torque load.

The

preload applying members

40a and 40b are annular rubbers made of an elastomer and centered on the central axis AX. The preload-applying member 40a is disposed between the outer race 31a of the first bearing 30a and the plate 18. The preload-applying member 40b is disposed between the outer ring 31b of the second bearing 30b and the stepped surface 101c of the first body 101. That is, the

pre-pressure applying members

40a and 40b are arranged on the rotation sides of the first bearing 30a and the second bearing 30b in the central axis AX direction. After being mounted to the power transmission device 1, the

preload application members

40a and 40b are subjected to a compressive load in the direction of the central axis AX, and press the

outer rings

31a and 31b of the first bearing 30a and the second bearing 30 b.

The preload-applying

members

40a and 40b are disposed on both sides of the first bearing 30a and the second bearing 30b in the direction of the central axis AX. The first bearing 30a and the second bearing 30b are displaceable in the direction of the central axis AX. Thus, when the distance in the central axis AX direction between the plate 18 and the step surface 101c is not a predetermined length, in other words, when there is a manufacturing error in the first body 101 and the second body of the housing 100, the preload-applying

members

40a, 40b can absorb the error. Therefore, even if there is a manufacturing error in the first body 101 and the second body of the housing 100, the preload amounts of the first bearing 30a and the second bearing 30b do not vary. When a large impact load in the direction of the central axis AX acts on the rack 88b, the preload-applying

members

40a and 40b can absorb the impact load. Further, the preload-applying

members

40a and 40b suppress vibration in the central axis AX direction around the ball screw device 10, and so-called knocking noise is also reduced.

As described above, comprising: a housing 100; a ball screw device 10 having a nut 13 housed in the housing 100, a screw shaft 11 penetrating the nut 13, and balls 15 disposed between the nut 13 and the screw shaft 11; a first bearing 30a and a second bearing 30b provided between the housing 100 and the nut 13 and arranged adjacent to each other in a direction of the central axis AX parallel to the central axis AX of the nut 13 so as to face each other; and preload-applying

members

40a, 40b that apply preload to the first bearing 30a and the second bearing 30b, wherein the first bearing 30a and the second bearing 30b each have an

outer ring

31a, 31b, the

outer rings

31a, 31b are fitted to the housing 100 and spaced apart from each other in the direction of the central axis AX, the preload-applying

members

40a, 40b press the

outer rings

31a, 31b in the direction in which the

outer rings

31a, 31b are brought close to each other, and a gap S is formed between the

outer rings

31a, 31 b.

If there is a dimensional error in the

outer rings

31a, 31b in the direction of the central axis AX, the gap S between the

outer rings

31a, 31b changes, or the preload-applying

members

40a, 40b deform, absorbing the error. Therefore, the outer ring raceway surfaces 31c and 31d are not displaced in the direction of the central axis AX, and the loads acting on the rolling

elements

35a and 35b are only loads applied by being pressed by the

preload application members

40a and 40b, so that a predetermined preload amount can be obtained. Thereby, the bearing torque is stabilized. The first bearing 30a and the second bearing 30b are disposed facing each other with a small distance between the points of action. That is, the first bearing 30a and the second bearing 30b are low in rigidity with respect to moment load. Therefore, the moment load input to the ball screw device 10 is reduced, and the occurrence of the abnormal noise is suppressed.

Further,

grease grooves

36a and 36b recessed radially inward are formed in the outer peripheral surfaces of the

outer rings

31a and 31b of the power transmission device 1. This ensures a larger amount of grease, improves the sliding properties of the

outer rings

31a and 31b, and prevents frictional heat from being generated. Therefore, the

outer rings

31a and 31b can be prevented from thermally expanding and varying the preload amount.

In the power transmission device, the

pre-pressure applying members

40a and 40b are disposed on the rotation sides of the first bearing and the second bearing. Thus, the

preload applying members

40a and 40b can absorb manufacturing errors of the case 100 in the direction of the central axis AX, and can prevent variations in the amount of preload.

In embodiment 1, an intersection LA1 of the extension LC1 of the contact angle of the first bearing 30a and the central axis AX and an intersection LA2 of the extension LC2 of the contact angle of the second bearing 30b and the central axis AX overlap each other, but the embodiment is not limited to this. Next, modification 1 and modification 2 in which intersection LA1 does not overlap intersection LA2 will be described.

Modification example 1

Fig. 6 is a sectional view of a power transmission device according to modification 1. In the following description, the same components as those described in the above embodiment are denoted by the same reference numerals, and redundant description thereof is omitted.

The power transmission device 1A of modification 1 differs from the power transmission device 1 of embodiment 1 in the following respects. In the power transmission device 1A of modification 1, the contact angle formed by the extended line LC3 of the contact angle of the first bearing 30a and the reference line CNa is θ 3. In the power transmission device 1A of modification 1, the contact angle formed by the extended line LC4 of the contact angle of the second bearing 30b and the reference line CNb is θ 4.

Specifically, the contact angle θ 3 formed by the extension LC3 of the contact angle of the first bearing 30a and the reference line CNa is larger than the contact angle θ 1 of embodiment 1. The contact angle θ 4 between the extension LC4 of the contact angle of the second bearing 30b and the reference line CNb is larger than the contact angle θ 2 in embodiment 1. Thus, the extension line LC3 of the contact angle of the first bearing 30a and the extension line LC4 of the contact angle of the second bearing 30b intersect before reaching the central axis AX as they approach the central axis AX from the centers C1 and C2 of the rolling

elements

35a and 35 b. After the intersection, the extended lines LC3, LC4 are spaced apart from each other as approaching the central axis AX. Then, on the center axis AX, an intersection LA3 (operating point of the first bearing 30 a) of an extension LC3 of the contact angle of the first bearing 30a and the center axis AX and an intersection LA4 (operating point of the second bearing 30 b) of an extension LC4 of the contact angle of the second bearing 30b and the center axis AX are not overlapped with each other. Therefore, the first bearing 30a and the second bearing 30b support the ball screw device 10 at two points of the intersection LA3 and the intersection LA 4. Further, in this example, the action point pitch (the distance between intersection point LA3 and intersection point LA 4) is still shorter than in the case of the back-to-back configuration. The rigidity with respect to the moment load can be reduced.

Modification 2

Fig. 7 is a sectional view of a power transmission device according to modification 2. The power transmission device 1B of modification 2 differs from the power transmission device 1 of embodiment 1 in the following respects. In the power transmission device 1B of modification 2, the contact angle formed by the extended line LC5 of the contact angle of the first bearing 30a and the reference line CNa is θ 5. In the power transmission device 1B of modification 2, the contact angle formed by the extended line LC6 of the contact angle of the second bearing 30B and the reference line CNb is θ 6.

Specifically, the contact angle θ 5 formed by the extension LC5 of the contact angle of the first bearing 30a and the reference line CNa is smaller than the contact angle θ 1 of embodiment 1. The contact angle θ 6 between the extension LC6 of the contact angle of the second bearing 30b and the reference line CNb is smaller than the contact angle θ 2 in embodiment 1. Thus, the extension line LC5 of the contact angle of the first bearing 30a and the extension line LC6 of the contact angle of the second bearing 30b approach the central axis AX from the centers C1 and C2 of the rolling

elements

35a and 35b, but do not intersect before reaching the central axis AX. But directly intersects the central axis AX. Therefore, the first bearing 30a and the second bearing 30b support the ball screw device 10 at two points, i.e., an intersection LA5 (action point of the first bearing 30 a) of an extension LC5 of the contact angle of the first bearing 30a and the central axis AX, and an intersection LA6 (action point of the second bearing 30 b) of an extension LC6 of the contact angle of the second bearing 30b and the central axis AX. In such an example, the shorter the point of action spacing (distance between intersection point LA5 and intersection point LA 6) is, the lower the stiffness with respect to moment loading.

Embodiment mode 2

Fig. 8 is a sectional view of the power transmission device according to embodiment 2. A power transmission device 1C according to embodiment 2 differs from the power transmission device 1 according to embodiment 1 in that an inner race 37 is provided in place of the inner race 33a of the first bearing 30a and the inner race 33b of the second bearing 30b, which are integrally formed.

The inner ring 37 includes double-row inner ring raceway surfaces 33c and 33d formed on the outer peripheral surface, and a shoulder groove 37a projecting radially outward from between the inner ring raceway surfaces 33c and 33 d. The inner ring 37 is fitted to the outer peripheral surface 13a of the nut 13. The first direction side end surface of the inner ring 37 contacts the wall portion 13b of the nut 13. The second direction side end surface of the inner ring 37 is in contact with the positioning member 17. Thereby, the inner ring 37 is positioned in the center axis AX direction by the positioning member 17 and the nut 13. As described above, the power transmission device 1C further includes the inner race 37 having the inner race raceway surface (first inner race raceway surface) 33C on which the rolling elements 35a roll between itself and the outer race 31a of the first bearing 30a, and having the inner race raceway surface (second inner race raceway surface) 33d on which the rolling elements 35b roll between itself and the outer race 31b of the second bearing 30 b. This can avoid the

inner rings

33a and 33b from being mounted on the nut 13, and reduce the number of mounting steps.

Embodiment 3

Fig. 9 is a sectional view of a power transmission device according to embodiment 3. A power transmission device 1D according to embodiment 3 is different from the power transmission device 1 according to embodiment 1 in that it includes a nut 13B integrally formed with inner rings 33a and 33B. That is, in the ball screw device 10B, the outer peripheral surface 13a of the nut 13B is formed with double-row inner-ring raceway surfaces 33c and 33d and a shoulder groove 37B projecting outward in the radial direction from between the inner-ring raceway surfaces 33c and 33 d. The inner race raceway surfaces 33c and 33d are subjected to hardening treatment such as bulk quenching, carburizing treatment, and high frequency treatment.

As described above, in the power transmission device 1D, the two hardened inner race raceway surfaces 33c and 33D on which the rolling elements 35a and 35B roll are formed on the outer peripheral surface of the nut 13B. This makes it possible to omit the

inner rings

33a and 33b, and to achieve a reduction in the size of the power transmission device 1D in the radial direction. The surfaces of the inner race raceway surfaces 33c and 33d are heat-treated to have a certain hardness, and the durability is improved.

Embodiment 4

Fig. 10 is a sectional view of a power transmission device according to embodiment 4. The power transmission device 1E of embodiment 4 differs from the power transmission device 1D of embodiment 3 in the following respects. In the power transmission device 1E according to embodiment 4, the

grease grooves

36a and 36b are not formed in the outer circumferential surfaces of the outer ring 31a of the first bearing 30a and the outer ring 31b of the second bearing 30 b. On the outer peripheral surfaces of the outer ring 31a of the first bearing 30a and the outer ring 31b of the second bearing 30b, recesses 38a and 38b extending in the circumferential direction are formed. O-

rings

50a and 50b are provided between the outer ring 31a of the first bearing 30a and the outer ring 31b of the second bearing 30b, respectively, and the inner circumferential surface 101b of the first body 101.

The

recesses

38a, 38b are grooves for receiving the O-

rings

50a, 50 b. Thus, when the

outer rings

31a and 31b slide in the central axis AX direction, the O-

rings

50a and 50b are displaced in the central axis AX direction together with the

outer rings

31a and 31 b. Further, outer circumferential portions of the O-

rings

50a and 50b project radially outward from outer circumferential surfaces of the

outer rings

31a and 31b, and elastically abut against an inner circumferential surface 101b of the first body 101.

As described above, in the power transmission device 1E, the O-

rings

50a and 50b are provided between the outer peripheral surfaces of the

outer rings

31a and 31b and the casing 100. Thereby, the radial vibration of the ball screw device 10B is absorbed by the O-rings 50a and 50B, and the occurrence of so-called knocking noise is suppressed.

Embodiment 5

Fig. 11 is a sectional view of a power transmission device according to embodiment 5. The power transmission device 1F of embodiment 5 differs from the power transmission device 1D of embodiment 3 in the following respects. In the power transmission device 1F according to embodiment 5, the

grease grooves

36a and 36b are not formed in the outer circumferential surfaces of the outer ring 31a of the first bearing 30a and the outer ring 31b of the second bearing 30 b. Further, a cylindrical cushion member 51 is disposed on the inner peripheral side of the inner peripheral surface 101b of the first body 101. In addition, a preload application member 41 is provided instead of the

preload application members

40a and 40 b.

The cushion member 51 is a cylindrical member formed of rubber or resin. The cushion member 51 is fitted into the inner peripheral surface 101b of the first body 101 and fixed to the first body 101. The outer ring 31a of the first bearing 30a and the outer ring 31b of the second bearing 30b are clearance-fitted to the cushion member 51, and are slidable in the central axis AX direction relative to the cushion member 51.

The preload applying member 41 includes an annular rubber 41a, and

cores

41b and 41c vulcanization-bonded to the rubber 41 a. The rubber 41a is compressed in the central axis AX direction, thereby pressing the outer ring 31a of the first bearing 30 a. The

cores

41b and 41c are used to maintain the shape of the rubber 41 a. The outer peripheral portion of the core 41c extends radially outward relative to the rubber 41a and abuts against the inner peripheral surface 101b of the first body 101. Thereby restricting the rubber 41a from being displaced radially outward.

In addition, only one preload-applying member 41 is provided, which applies a constant-pressure preload to the first bearing 30a and the second bearing 30 b.

As described above, in the power transmission device 1F, the cylindrical cushion material 51 is provided between the outer peripheral surfaces of the

outer rings

31a and 31b and the casing 100, and the outer peripheral surfaces of the

outer rings

31a and 31b are covered with the cushion material 51. This cushion material 51 can absorb large vibration that cannot be completely absorbed by the O-ring, and can reliably suppress the occurrence of so-called knocking noise.

Further, since the constant-pressure preload is applied to the first bearing 30a and the second bearing 30b by only one preload application member 41, the dimension of the power transmission device 1F in the direction of the central axis AX is reduced, and the device is downsized. Even when there is a dimensional error in the direction of the central axis AX in the first bearing 30a or the second bearing 30b, the dimensional error can be absorbed by the preload application member 41, and the bearing torque can be stabilized.

Modification 3

Fig. 12 is a sectional view of a power transmission device according to modification 3. A power transmission device 1G of modification 3 differs from the power transmission device 1F of embodiment 5 in that a preload application member 45 is used instead of the preload application member 41.

The preload-applying member 45 is a spacer in which the dimension C in the direction of the central axis AX is adjusted. That is, in modification 3, the preload is applied to the first bearing 30a and the second bearing 30b by the positioning preload. Examples of the material of the pre-press application member 45 include iron, aluminum alloy, magnesium alloy, and resin. The dimension C of the preload-applying member 45 in the direction of the central axis AX is represented by the following formula 1.

C ═ δ + B- (a- Δ) … (formula 1)

In formula 1, a is a dimension of the first bearing 30a and the second bearing 30b in the direction of the central axis AX in a state where the preload is not applied. (a- Δ) is a dimension of the first bearing 30a and the second bearing 30b in the direction of the central axis AX in a state where the preload is applied. B is the distance between the stepped surface 101c of the housing 100 and the plate member 18. σ is an elastic deformation amount generated when the preload application member 45 is changed from a state in which a preload is not applied to a state in which a preload is applied.

As described above, according to the power transmission device 1G of modification 3, by appropriately selecting the material of the preload applying member 45 as the spacer, it is possible to alleviate the change in the preload amount due to the temperature change. Specifically, the case 100 and the

outer rings

31a and 31b expand due to temperature rise, and then increase in size in the direction of the central axis AX. Assuming that the case 100 is made of an aluminum alloy and the

outer rings

31a, 31b are made of bearing steel, if the preload-applying member 45 made of iron is selected, since the linear expansion coefficient of the aluminum alloy is larger than that of iron, the amount of expansion of the preload-applying member 45 is smaller than that of the case 100, so that the amount of preload applied by positioning preload is decreased. Therefore, by selecting the preload application member 45 made of the same material as the case 100 made of the aluminum alloy, it is possible to alleviate the decrease in the preload amount due to the temperature change. Further, according to the above configuration, the variation in the preload amount can be more favorably relaxed than in the case where the preload applying member 45 made of resin is selected.

Embodiment 6

Fig. 13 is a sectional view of a power transmission device according to embodiment 6. The power transmission device 1H of embodiment 6 differs from the power transmission device 1F of embodiment 5 in the following respects. The power transmission device 1G according to embodiment 6 includes a preload application member 42 in place of the preload application member 41. The outer race 31a of the first bearing 30a is formed with a projection 31 e. An inner peripheral seal member 60 is provided on the inner peripheral side of the outer race 31a of the first bearing 30 a.

The pre-load applying member 42 is an elastic body formed of a metal material. The preload-applying member 42 is a disc spring that is inclined so as to be positioned radially outward toward the second direction side of the central axis AX. The first direction side end 42a of the pre-pressure applying member 42 abuts against the panel 18. The second-direction-side end portion 42b of the preload-applying member 42 abuts against the outer ring 31a of the first bearing 30a to press the outer ring 31 a. In addition, as an embodiment, a wave washer may be used instead of the disc spring.

The projection 31e projects toward the first direction side from an end surface of the outer ring 31a facing the first direction side. The projection 31e is located radially outward with respect to the pre-pressure applying member 42. Further, the boss 31e is provided between the inner peripheral surface 101b of the first body 101 and the pre-pressure applying member 42. Therefore, the end 42b of the preload-applying member 42 abuts against the inner peripheral surface of the boss 31 e.

The inner peripheral seal member 60 is an annular rubber fitted into the inner peripheral side of the outer ring 31 a. The radially inner end of the inner peripheral seal member 60 is in sliding contact with the outer peripheral surface of the nut 13B.

As described above, in the power transmission device 1H, the preload-applying member 42 is an elastic body of a metal material, and the outer ring 31a has the projection 31e that projects from the end surface thereof and is provided between the case 100 and the preload-applying member 42. Thereby, the elastic body of the metal material is in contact with the projection 31 e. Thereby, it is possible to prevent the case where the preload-applying member 42 contacts the case 100 to cause the case 100 to be worn.

The power transmission device 1H further includes an inner peripheral seal member 60 for closing a gap between the inner peripheral surface of the outer ring 31a of the first bearing 30a and the opposing surface (the outer peripheral surface 13a of the nut 13B) to the inner peripheral surface of the outer ring 31 a. Thus, the first direction side of the rolling elements 35a is covered by the inner peripheral seal member 60, and foreign matter is less likely to enter. Particularly, the pulley device 20 is disposed on the first direction side of the rolling elements 35 a. Abrasion powder may be generated by abrasion between the meshing portions of the drive pulley 21 and the transmission belt 25 and abrasion between the meshing portions of the driven pulley 23 and the transmission belt 25, but this structure makes it possible to prevent the abrasion powder from entering the inside of the first bearing 30 a.

Embodiment 7

Fig. 14 is a sectional view of a power transmission device according to embodiment 7. A power transmission device 1I according to embodiment 7 differs from the power transmission device 1G according to embodiment 6 in that a preload application member 43 and an inner peripheral seal member 61 that are integrally formed are provided instead of the preload application member 42 and the inner peripheral seal member 60 that are separately formed.

The preload applying member 43 includes a preload elastomer 43a made of rubber, and preload

cores

43b and 43c vulcanized and bonded to the preload elastomer 43 a. The inner peripheral seal member 61 includes an inner peripheral seal elastic body 62 made of rubber that is in sliding contact with the outer peripheral surface of the nut 13B, and an inner peripheral seal core 63 that supports the inner peripheral seal elastic body 62. The inner peripheral sealing core 63 has an inner peripheral fitting portion 63a that is fitted to the inner peripheral surface of the outer ring 31 a. The preload core 43b is continuous with the inner peripheral fitting portion 63a, and the preload core 43b is formed integrally with the inner peripheral sealing core 63.

As described above, in the power transmission device 1I, the inner peripheral seal member 61 includes: an inner periphery sealing core 63 disposed on the inner periphery side of the outer ring 31 a; and an inner peripheral sealing elastic body 62 supported by the inner peripheral sealing core 63 and in sliding contact with the nut 13B as an opposing surface, the preload-applying member 43 including: a preload elastic body 43a for generating preload; and preload

cores

43b and 43c that support the preload elastic body 43a, wherein the inner peripheral seal core 63 includes an inner peripheral fitting portion 63a that is fitted to the inner peripheral surface of the outer ring 31a, and the inner peripheral seal core 63 is formed integrally with the preload core 43 b. Thus, the two members, i.e., the inner peripheral seal member 61 and the preload application member 43, can be attached by the operation of fitting the inner peripheral fitting portion 63a to the inner peripheral side of the outer ring 31 a. Thereby reducing man-hours for the mounting work. In embodiment 7, the preload elastic body 43a made of rubber is used, but an elastic body made of a metal material may be used.

Embodiment 8

Fig. 15 is a sectional view of a power transmission device according to embodiment 8. The power transmission device 1J according to embodiment 8 differs from the power transmission device 1I according to embodiment 7 in that a preload application member 44 is provided in place of the preload application member 43, and an outer peripheral sealing elastic body 64 is further provided.

The preload-applying member 44 includes a disc spring 44a and a preload mandrel 44b that supports the disc spring 44 a. The preload core 44b has a base surface 44c provided between the disc spring 44a and the first body 101. The preload mandrel 44b is formed integrally with the inner peripheral sealing mandrel 63. The outer peripheral sealing elastic body 64 is made of rubber, and is bonded to the outer peripheral surface of the base surface 44c by vulcanization. The outer peripheral surface of the outer peripheral sealing elastic body 64 abuts against the inner peripheral surface 101b of the first body 101 to close a gap between the outer peripheral surface of the outer ring 31a and the inner peripheral surface 101b of the first body 101.

As described above, the power transmission device 1J includes the outer peripheral sealing elastic body 64 for closing the gap between the outer peripheral surface of the outer ring 31a and the inner peripheral surface 101b of the casing 100, and the outer peripheral sealing elastic body 64 is fixed to the outer peripheral surface of the preload core 44b and is in sliding contact with the inner peripheral surface 10b of the casing 100. The grease is less likely to leak from between the outer ring 31a and the housing 100 by the outer peripheral sealing elastic body 64. The outer peripheral sealing elastic body 64 can absorb the radial vibration of the outer ring 31a, and suppress the occurrence of so-called rattling noise. Further, by the work of fitting the inner peripheral seal core 63 into the inner peripheral side of the outer ring 31a, the three members of the inner peripheral seal member 61, the preload application member 44, and the outer peripheral seal elastic body 64 can be mounted together, and the man-hours for the mounting work can be reduced.

Embodiment 9

Fig. 16 is a sectional view of a power transmission device according to embodiment 9. Fig. 17 is a schematic view of only the pre-compression applying member and the high load absorbing portion taken out and viewed from the central axis AX direction. As shown in fig. 16, a power transmission device 1K according to embodiment 9 is different from the power transmission device 1C according to embodiment 2 in that a pair of

annular members

65a and 65b are provided instead of the

preload applying members

40a and 40 b.

The

annular members

65a and 65b are formed in plane symmetry with respect to a virtual plane having the central axis AX as a vertical line. Therefore, among the

annular members

65a and 65b, the annular member 65a disposed on the first direction side of the first bearing 30a will be described as a representative example, and the description of the annular member 65b will be omitted.

The annular member 65a includes a core 66 and a rubber 67 vulcanized and bonded to the core 66. The core 66 includes: an outer peripheral fitting portion 66a fitted to the outer peripheral surface of the outer ring 31a, an abutting portion 66b abutting against the first direction side end surface of the outer ring 31a, and an extending portion 66c extending radially inward from the abutting portion 66 b. The outer peripheral fitting portion 66a is disposed in the recess 39 formed in the outer peripheral surface of the outer ring 31 a. Therefore, the outer peripheral fitting portion 66a is positioned radially inward of the outer peripheral surface of the outer ring 31 a.

The rubber 67 includes: an outer periphery sealing elastic body 67a formed on the outer periphery side of the outer periphery fitting portion 66 a; a high load absorbing portion 67b formed on a side surface of the abutment portion 66b on the first direction side; a preload-applying member 67c that protrudes from the high-load absorbing portion 67b toward the first direction side; and an inner peripheral sealing elastic body 67d that extends radially inward along the extension 66 c. The outer peripheral sealing elastic body 67a, the high load absorbing portion 67b, the preload applying member 67c, and the inner peripheral sealing elastic body 67d are integrally connected.

The outer peripheral sealing elastic body 67a is in sliding contact with the inner peripheral surface 101b of the first body 101. Thus, grease is less likely to leak from between the first body 101 and the outer ring 31 a. Thereby, the outer peripheral sealing elastic body 67a can absorb the radial vibration of the outer ring 31a, thereby suppressing the occurrence of so-called rattling noise. The inner peripheral sealing elastic body 67d is in sliding contact with the outer peripheral surface of the inner ring 37. This can prevent foreign matter from entering the first bearing 30 a.

Before the mounting, the high load absorbing portion 67b and the pre-pressure applying member 67c are formed to have the same thickness in the central axis AX direction. The radial length of the high load absorption portion 67b is L1. The pre-pressure applying member 67c has a radial length L2. Therefore, the high load absorbing portion 67b is formed to be longer than the preload applying member 67c in the radial length. That is, the high load absorbing portion 67b has a larger cross-sectional area than the preload application member 67c when cut along the central axis AX.

The high load absorbing portion 67b and the preload application member 67c are attached between the plate 18 and the outer ring 31a, and receive a compression load in the direction of the center axis AX. Therefore, the preload application member 67c having a small cross-sectional area is deformed more than the high load absorbing portion 67 b. Thereby, the preload application member 67c presses the outer ring 31a to apply a preload to the first bearing 30 a. On the other hand, when a large load acts on the rack 88b along the central axis AX, the high load absorbing portion 67b is deformed to absorb the load. As shown in fig. 17, the high load absorbing portion 67b is formed in a ring shape centered on the central axis AX. The preload-applying member 67c includes a plurality of convex portions 67e, and the convex portions 67e are formed in a rectangular shape when viewed from the central axis AX direction.

As described above, the power transmission device 1K includes: a core 66 fixed to the

outer rings

31a and 31b of either the first bearing 30a or the second bearing 30 b; and an inner peripheral sealing elastic body 67d that is supported by the core 66 and closes the inner peripheral sides of the

outer rings

31a, 31b, wherein the core 66 has a cylindrical outer peripheral fitting portion 66a that fits onto the outer peripheral surfaces of the

outer rings

31a, 31b, and the outer peripheral surfaces of the

outer rings

31a, 31b are formed with a recess 39 that is recessed radially inward and that accommodates the outer peripheral fitting portion 66 a. This prevents the outer peripheral fitting portion 66a from abutting against the housing 100 and obstructing the sliding of the outer ring 31 a.

The power transmission device 1K includes an outer peripheral sealing elastic body 67a for closing a gap between the outer peripheral surfaces of the

outer rings

31a and 31b and the inner peripheral surface 101b of the housing 100, and the outer peripheral sealing elastic body 67a is fixed to the outer peripheral surface of the outer peripheral fitting portion 66a and is in sliding contact with the inner peripheral surface 101b of the housing 100. The outer peripheral sealing elastic body 67a can suppress leakage of grease from between the outer ring 31a and the housing 100, and ensure the slidability of the outer ring 31 a. Thus, the outer peripheral sealing elastic body 67a absorbs the radial vibration of the outer ring 31a, and the occurrence of so-called rattling noise is suppressed. Further, since the outer peripheral sealing elastic body 67a is also attached when the core 66 is attached to the outer ring 31a, the number of steps for the attachment work is reduced.

The power transmission device 1K includes a rubber high-load absorbing portion 67b provided between the preload applying member 67c and the

outer rings

31a and 31b to absorb a high load in the direction of the central axis AX; the pre-pressure-applying member 67c is made of rubber, and has a smaller cross-sectional area cut in the direction of the central axis AX than the high-load-absorbing portion 67B. Thus, after the high load absorbing portion 67b and the preload application member 67c are attached, the preload application member 67c deforms to press the outer ring 31a, thereby applying preload to the first bearing 30a and the second bearing 30 b. On the other hand, when a high load is applied in the direction of the central axis AX, the high load absorbing portion 67b absorbs the high load. Thereby avoiding the situation where the preload-applying member 67c is broken by a high load.

The preload-applying member 67c of the power transmission device 1K includes a plurality of protrusions 67e arranged at intervals in the circumferential direction. Therefore, by changing the number of the convex portions 67e, the preload amount of the preload applying member 67c can be adjusted. The outer peripheral sealing elastic body 67a, the high load absorbing portion 67b, the preload application member 67c, and the inner peripheral sealing elastic body 67d are formed integrally by the rubber 67 in a continuous manner, but may be formed of another elastic body or a combination of a plurality of materials. For example, the preload application member 67c may be formed of a material such as a resin or a mixed material, or may be formed of an elastic member such as a disc spring. The mixed material may be a mixture of rubber and resin, and the hardness of the material can be changed by adjusting the mixing ratio of the rubber and the resin. Further, the high load absorbing portion 67b may be formed using a material different from that of the preload applying member 67 c.

Description of the symbols

1. 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1I, 1J, 1K: power transmission device

10. 10B: ball screw device

11: screw shaft

13: nut

15: ball bearing

17: positioning member

18: plate member

20: belt wheel device

30 a: first bearing

30 b: second bearing

31a, 31 b: outer ring

31 e: projection

33a, 33b, 37: inner ring

35a, 35 b: rolling body

36a, 36 b: lubricating grease tank

38a, 38 b: concave part

40a, 40b, 41, 42, 43, 44, 45, 67 c: pre-pressure applying member

51: buffer piece

60. 61: inner peripheral sealing member

64: elastic body for outer periphery sealing

66: core rod

65a, 65 b: ring-shaped member

67 a: elastomer for outer periphery sealing

67 b: high load absorbing part

67 d: elastic body for inner peripheral sealing

80: electric power steering apparatus

100: shell body

101: first main body

101 b: inner peripheral surface

103: second body

105: third body

AX: center shaft

CNa, CNb: reference line

LC1, LC2, LC3, LC4, LC5, LC 6: extension of contact Angle

Claims

1. A power transmission device characterized by comprising:

a housing;

a ball screw device having a nut accommodated in the housing, a screw shaft penetrating the nut, and balls disposed between the nut and the screw shaft;

a first bearing and a second bearing which are provided between the housing and the nut and are arranged adjacent to each other in a central axis direction parallel to a central axis of the nut so as to face each other; and

a preload-applying member that applies preload to the first bearing and the second bearing,

the first bearing and the second bearing each include an outer ring that is fitted to the housing and spaced apart from each other in a center axis direction,

the preload-applying member presses the outer rings in a direction in which the outer rings approach each other, and a gap is formed between the outer rings.

2. The power transmission device according to claim 1, characterized by further comprising:

and an inner ring having a first inner ring raceway surface on which the rolling elements roll between the inner ring and the outer ring of the first bearing, and having a second inner ring raceway surface on which the rolling elements roll between the inner ring and the outer ring of the second bearing.

3. The power transmission device according to claim 1,

two hardened inner ring raceway surfaces on which the rolling elements roll are formed on the outer peripheral surface of the nut.

4. The power transmission device according to any one of claims 1 to 3,

the outer peripheral surface of the outer ring is formed with a grease groove recessed radially inward.

5. The power transmission device according to any one of claims 1 to 4,

an O-ring is provided between the outer peripheral surface of the outer ring and the housing.

6. The power transmission device according to any one of claims 1 to 4,

a cylindrical buffer member is disposed between the outer peripheral surface of the outer ring and the housing,

the outer peripheral surface of the outer ring is covered with the buffer member.

7. The power transmission device according to any one of claims 1 to 6,

the pre-load applying member is an elastic body of a metal material,

the outer ring has a projection projecting from an end surface and provided between the housing and the pre-pressure applying member.

8. The power transmission device according to any one of claims 1 to 6,

either one of the first bearing and the second bearing is provided with an inner peripheral seal member that closes a gap between an inner peripheral surface of the outer ring and an opposing surface that opposes the inner peripheral surface of the outer ring.

9. The power transmission device according to claim 8,

the inner peripheral seal member includes:

an inner periphery sealing core bar disposed on an inner periphery side of the outer ring; and

an inner peripheral sealing elastic body supported by the inner peripheral sealing core and slidably contacting the opposing surface,

the pre-pressure applying part includes:

an elastic body for pre-compaction for generating pre-compaction: and

a pre-pressing core bar for supporting the pre-pressing elastic body,

the inner periphery sealing core has an inner periphery fitting portion fitted to the inner periphery of the outer ring, and is formed integrally with the preload core.

10. The power transmission device according to claim 9, characterized by comprising:

an outer peripheral sealing elastic body that closes a gap between an outer peripheral surface of the outer ring and an inner peripheral surface of the housing,

the outer peripheral sealing elastic body is fixed to an outer peripheral surface of the preload core and is in sliding contact with an inner peripheral surface of the housing.

11. The power transmission device according to any one of claims 1 to 4, characterized by comprising:

a core bar fixed to an outer ring of either one of the first bearing and the second bearing; and

an inner peripheral sealing elastic body supported by the core bar to close an inner peripheral side of the outer ring,

the core has a cylindrical outer peripheral fitting portion fitted to the outer peripheral surface of the outer ring,

the outer ring has a recess formed in an outer peripheral surface thereof, the recess being recessed radially inward for receiving the outer peripheral fitting portion.

12. The power transmission device according to claim 11, characterized by comprising:

the outer peripheral sealing elastic body is fixed to an outer peripheral surface of the outer peripheral fitting portion and is in sliding contact with an inner peripheral surface of the housing.

13. The power transmission device as claimed in claim 12, characterized by comprising:

a high load absorbing portion provided between the preload applying member and the outer ring, for absorbing a high load in the center axis direction,

the cross-sectional area of the preload-applying member cut in the direction of the central axis is smaller than the high-load absorbing portion.

14. The power transmission device according to claim 13,

the pre-pressure applying member has a plurality of protrusions arranged to be spaced apart from each other in a circumferential direction.